1. Field of the Invention
The present invention relates to a mobile communication system. More particularly, the present invention relates to a location sensing system and method for a mobile communication system that is capable of providing location sensing service with the support of mobile nodes.
2. Description of the Related Art
Location sensing is one of the more important techniques in which recent mobile communication systems operate. Triangulation, scene analysis, and proximity are the three principal techniques for automatic location sensing.
Of the three techniques, triangulation location sensing technique computes the position of a mobile node by measuring its distance from three anchor nodes. In more detail, the mobile node measures the time-of-arrival to the three anchor nodes and determines the point at which three circles drawn with the radii calculated on the basis of the time-of-arrival as the location of the mobile node.
With regard to another of the three techniques, the scene analysis location sensing technique utilizes features of a scene sensed from a particular vantage point to draw conclusions about the location of an object in the scene. The scene analysis is categorized into a static scene analysis, which compares the observed image with reference images stored in a database, and a differential scene analysis, which tracks the difference between successive scenes to estimate location.
Finally, the third technique, a proximity location sensing technique, entails determining when the mobile node is “near” another node. There are three general approaches to sensing proximity: detecting physical contact with an object, monitoring wireless cellular access points which monitoring when a mobile device is in range of one or more access points in a cellular network, and observing automatic ID systems through the operation of various identification systems.
We refer now to FIG. 1, which is a schematic diagram illustrating a conventional triangular location sensing technique.
The triangular location sensing is known as the most accurate location sensing technique. Referring to the example in FIG. 1, a mobile node 100 communicates with three anchor nodes 110, 130, and 150.
In order to locate the mobile node 100 with the triangular location sensing technique, at least three anchor nodes have to be within the transmission range of the mobile node 100. Also, in view of the anchor nodes, the mobile node 100 should be within the transmission ranges of the respective anchor nodes 110, 130, and 150.
In other words, if the mobile node 100 is out of the range of any one of three anchor nodes 110, 130, and 150, it is impossible to locate the mobile node using the triangular location sensing technique. Also, in a case where at least one of three anchor nodes 110, 130, and 150 involved in an ongoing triangular location sensing is temporarily erroneous, the mobile node 100 fails computing its location.
Accordingly, there is a need for an improved triangular location sensing method that is capable of securing stability and reliability of location service even when the mobile node does not find three anchor nodes or an anchor node involved in the ongoing triangular location sensing process is erroneous.